A generalization of the gravitational lens technique uses large numbers of faint background galaxies

A generalization of the gravitational lens technique uses large numbers of faint background galaxies

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A generalization of the gravitational lens technique uses large numbers of faint background galaxies to probe the cluster potential. This was first tried for individual galaxies by Tyson et al. (1984 ApJLett 281, L59), and given new impetus by the discovery of luminous arcs in galaxy clusters (Lynds and Petrosian 1986 BAAS 18, 1014; Soucail et al. 1987 A&A 172, L14; 1988 A&A 191, L19). The redshifts of the arcs (an impressive feat) are much higher than the clusters, implicating gravitational lensing. Statistical models have been very successful in reproducing the occurrence and appearance of the arcs (as in, for example, Grossman and Narayan 1989 (ApJ 344, 637). The arcs in Abell 2218 show the effect quite intuitively (as discussed by Kneib et al 1996 ApJ 471, 643 and Smail et al 1996 ApJ 469, 508). This image is from the HST SM3A OV phase (how's that for stacked acronyms?). Notice the divergence of arcs around the bright galaxy to the lower left, showing that there is a significant concentration of total mass associated with it rather than just the cluster as a whole. A remarkable extension was introduced by Tyson et al. (1990 ApJLett 349, L1) who analyzed the images of faint galaxies around nearby clusters statistically and were able to derive not only masses but the mass distribution. Color selection allowed discrimination between faint cluster members and the distant background galaxies that will show this distortion. This approach, so- called weak lensing, can also be used statistically for individual galaxy masses. They find that the matter is only slightly more extended than the galaxy distribution; the dark matter in these
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This note was uploaded on 11/10/2011 for the course AST AST1002 taught by Professor Emilyhoward during the Fall '10 term at Broward College.

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A generalization of the gravitational lens technique uses large numbers of faint background galaxies

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